Terms

Purines

A class of nucleotides that includes adenine and guanine, which are characterized by a double-ring structure.

Pyrimidines

A class of nucleotides that includes cytosine, thymine (in DNA), and uracil (in RNA), characterized by a single-ring structure.

Complementary base pairing

The principle that adenine pairs with thymine (or uracil in RNA) and guanine pairs with cytosine in DNA.

Antiparallel

Refers to the orientation of the two strands of DNA that run in opposite directions.

Semiconservative

The method of DNA replication in which each new DNA molecule consists of one original strand and one new strand.

Replication fork

The Y-shaped region where the DNA double helix separates during replication.

DNA helicase

An enzyme that unwinds the DNA double helix during replication.

DNA polymerase

An enzyme that synthesizes new DNA strands by adding nucleotides based on the template strand.

Template strand

The strand of DNA that provides the pattern for replication or transcription.

Leading strand

The DNA strand that is synthesized continuously in the direction of the replication fork.

Lagging strand

The DNA strand that is synthesized discontinuously in short segments away from the replication fork.

Okazaki fragment

Short segments of DNA synthesized on the lagging strand during DNA replication.

DNA ligase

An enzyme that joins Okazaki fragments together to create a continuous DNA strand.

Transcription

The process of copying a segment of DNA into RNA.

Translation

The process of decoding mRNA to synthesize proteins.

Messenger RNA (mRNA)

The RNA molecule that carries the genetic information from DNA to the ribosome for protein synthesis.

Transfer RNA (tRNA)

The RNA molecule that carries amino acids to the ribosome during protein synthesis.

Ribosomes + ribosomal RNA

Cellular structures that facilitate the translation of mRNA into protein.

RNA polymerase

An enzyme that synthesizes RNA from a DNA template during transcription.

Promoter

A specific DNA sequence where RNA polymerase binds to initiate transcription.

Coding strand

The DNA strand that has the same sequence as the mRNA transcript, except for the substitution of uracil for thymine.

mRNA transcript

The RNA strand produced from the DNA template during transcription.

The genetic code

The set of rules by which information encoded in genetic material is translated into proteins.

Codon

A three-nucleotide sequence on mRNA that specifies an amino acid.

Start codon

The codon AUG in mRNA that signals the beginning of protein synthesis.

Stop codon

A codon that signals the termination of translation.

Anticodon

A three-nucleotide sequence on tRNA that is complementary to a codon on mRNA.

Polyribosome

A cluster of ribosomes translating the same mRNA strand simultaneously.

Initiation

The phase in transcription or translation where the process begins.

Elongation

The phase in transcription or translation where the RNA or protein strand is synthesized.

Termination

The phase in transcription or translation where the process ends.

Gene Mutation

A permanent alteration in the DNA sequence of a gene.

Mutagens

Agents that cause changes in DNA that can lead to mutations.

Spontaneous vs induced mutation

Spontaneous mutations occur naturally, while induced mutations result from exposure to external factors.

Point mutation vs frameshift mutation

Point mutations involve a change in a single nucleotide, while frameshift mutations involve insertions or deletions that alter the reading frame.

Base substitution

A type of point mutation where one nucleotide is replaced by another.

Addition

A type of mutation where one or more nucleotides are added to the DNA sequence.

Deletion

A type of mutation where one or more nucleotides are removed from the DNA sequence.

Ecosystem

A community of living organisms and their physical environment interacting as a system.

Biotic

Living components of an ecosystem.

Abiotic

Non-living chemical and physical factors in the environment.

Autotrophs

Organisms that produce their own food; photo-autotrophs use light, while chemo-autotrophs use chemical energy.

Heterotrophs

Organisms that obtain food by consuming other living things.

Herbivores

Organisms that eat plants.

Carnivores

Organisms that eat other animals.

Omnivores

Organisms that eat both plants and animals.

Detritivores

Organisms that feed on dead organic matter.

Energy Flow

The movement of energy through an ecosystem, originating from sunlight and transferred through food chains.

Chemical cycling

The movement of elements and compounds through living organisms and the environment.

Food web

A complex network of feeding relationships among various organisms in an ecosystem.

Food chain

A linear sequence of organisms through which nutrients and energy pass.

Trophic levels

The hierarchical levels in an ecosystem, consisting of producers, consumers, and decomposers.

Ecological pyramid

A graphical representation showing the relative amounts of energy or matter at different trophic levels.

Biogeochemical cycles

Natural pathways that cycle essential elements and compounds through the ecosystem.

Evaporation

The process by which water changes from liquid to gas.

Condensation

The process by which water vapor cools and changes back to liquid water.

Transpiration

The process by which water is absorbed by plants and released as vapor into the atmosphere.

Precipitation

Any form of water that falls from the atmosphere to the surface of the Earth.

The water cycle

The continuous movement of water on, above, and below the surface of the Earth.

The carbon cycle

The series of processes by which carbon compounds are interconverted in the environment.

Climate

The long-term average of weather conditions in a particular area.

Biome

A large geographical biotic unit, a major community of plants and animals with similar life forms and environmental conditions.

Tundra

A cold, treeless biome characterized by low-growing vegetation and short growing seasons.

Coniferous forests/Taiga

Biomes dominated by coniferous trees, typically found in cold climates.

Temperate deciduous forest

A biome characterized by four distinct seasons and trees that shed their leaves annually.

Tropical forest

A biome found near the equator, characterized by high rainfall and a diverse array of plants and animals.

Shrublands

Biomes characterized by shrubs and a Mediterranean climate.

Grasslands

Biomes where grass is the primary plant life; temperate grasslands have hot summers and cold winters, while savannas are warm with seasonal rainfall.

Desert

A biome characterized by low precipitation and extreme temperatures.

Streams/Rivers

Freshwater ecosystems characterized by flowing water.

Lakes

Freshwater bodies that are large and deep enough for stratification.

Wetlands

Areas where water covers the soil for part of the year, supporting diverse ecosystems.

Oceans

Large bodies of saltwater that cover about 71% of the Earth's surface.